1. Field of the Invention
The present invention relates to a lens barrier driving device that drives a lens barrier in a lens barrel mounted in an image pickup apparatus such as a silver film camera or an electronic camera, as well as the lens barrel and the image pickup apparatus.
2. Description of the Related Art
Many conventional cameras have lens barrels in which lens barriers are mounted. The lens barrier shuts off a surface of a photographic lens from the outside while pictures are not taken. This thus protects the photographic lens from attachment of sebum resulting from the user's touch or attachment of dust or the like to prevent optical performance from being degraded.
Available lens barrier driving methods include a method in which a photographer manually opens and closes or mounts and removes the lens barrier and a method in which the lens barrier is automatically opened when the camera is ready for shooting and closed when the camera is in a standby or power-off state. An example of a mechanism is shown below which automatically opens and closes the lens barrier.
FIG. 12A is an exploded perspective view showing the components of a lens barrel according to a conventional example. FIG. 12B is a perspective view showing the assembled lens barrel. FIGS. 13A and 13C are diagrams schematically showing how a driving mechanism operates to sink the lens barrel. FIGS. 13B and 13D are diagrams schematically showing how the driving mechanism operates to withdraw the lens barrel.
In FIGS. 12A to 13D, a first group barrel 100 holds a first lens group and internally has a mechanism that drives a lens barrier 111. A barrier driving lever 112 drivingly opens and closes the lens barrier 111. A barrier opening spring 113 always biases the lens barrier 111 in a direction in which it is opened. A barrier closing spring 115 biases the lens barrier 111 in a direction in which it is closed. A lens barrier driving plate 114 drives the lens barrier 111 in the closing direction. The lens barrier driving plate 114 has a hole portion 114a and a notch portion 114b. A tapered cam member 130a is disposed on a barrel base plate 130 to open and close the lens barrier 111. Reference numerals 116 and 117 denote a barrier cover and an external cap respectively.
Using an image pickup apparatus mounted with the lens barrel described above, when a photographer suspends or temporarily pauses shooting, the lens barrel including the first group barrel 100 is housed (sunken) in the image pickup apparatus main body. During transition to the housed state, an abutting member 112a of the barrier driving lever 112 abuts against a slope near a tip of the cam member 130a (see FIG. 13A). The abutting member 112a slidably moves on the slope of the cam member 130a to rotatively drive the barrier driving lever 112. Thus, the spring force charged in the barrier closing spring 115 applies a rotative driving force to the lens barrier driving plate 114. The rotative driving force is utilized to close the lens barrier 111.
Once the lens barrel is completely housed in the image pickup apparatus main body, the photographic lens is covered with the lens barrier 111. If the state in which the lens barrel is housed in the image pickup apparatus main body is transited to an image taking enabled state, the first group barrel 100 is gradually separated from the barrel base plate 130. At this time, the spring force charged in the barrier opening spring 113 is gradually released to pivot the barrier driving lever 112 counterclockwise in FIG. 13D. Pivoting of the barrier driving lever 112 causes rotation of the lens barrier driving plate 114 and counterclockwise rotation of the lens barrier 111 to perform an opening operation.
On the other hand, a lens barrier driving method has been proposed which drives the lens barrier utilizing cam drive on the basis of the relationship between the relative positions of a first and second lens groups (see, for example, Japanese Laid-Open Patent Publication No. H07-159855).
Another lens barrier driving method has been proposed which transmits the rotating force of the rotating barrel to a transmission member and utilizes the transmitted force to drive the lens barrier (see, for example, Japanese Laid-Open Patent Publication No. H10-186453).
Another lens barrier driving method has been proposed which drives the lens barrier utilizing cam drive on the basis of the relationship between the relative positions of a first and third lens groups (see, for example, Japanese Laid-Open Patent Publication No. H07-005547).
With the conventional technique shown in FIGS. 12A to 13D, the barrier driving lever 112 and the cam member 130a are arranged as follows. To reduce the size of the lens barrel, a penetrating area is formed in a part of a barrel such as a second or third group barrel (not shown) that holds another lens group so that the barrier driving lever 112 and cam member 130a can penetrate the penetrating area. Thus, with image taking enabled, appropriately arranging the lens groups results in a cavity in the penetrating area in the second or third group barrel, which area is penetrated by the barrier driving lever 112 and cam member 130a. 
This leads to a light leakage phenomenon in which external light travels through the cavity to an image forming surface, or ghosts caused by, for example, light reflected from an inner wall surface of the barrel. As a result, the optical performance may be degraded. To avoid this, the penetrating portion through which the barrier driving lever 112 and cam member 130a penetrate is provided in the direction of 12 o'clock with respect to the optical axis as observed from an object. This thus suppresses the adverse effect of light leakage. However, this structure imposes a restriction in constructing the barrel, thus reducing the degree of freedom of barrel design.
With the conventional technique described in Japanese Laid-Open Patent Publication No. H07-159855, if a lens configuration is adopted in which the first and second lens groups are brought closer to each other in an image taking area near a telescope end than when the lens barrel is sunken, the following mechanism is provided. No transmission member is provided between a barrier opening and closing ring and a cam member. Instead, a mechanism for allowing the cam member to escape is provided so as to prevent the cam member from engaging with the barrier opening and closing ring. This disadvantageously increases the number of parts required.
With the conventional technique described in Japanese Laid-Open Patent Publication No. H10-186453, the barrel holding the transmission member requires a gap corresponding to the stroke of rotation of the barrel. This may disadvantageously lead to light leakage.
The conventional technique described in Japanese Laid-Open Patent Publication No. H07-005547 reduces a variation in the spacing between the first and third lens groups in the image taking area. This technique further opens and closes the barrier using the transmission member for transmitting power to the lens group. This requires a space to be formed in the second lens group, located between the first and third lens groups, so as to allow the penetration of the transmission member. This may disadvantageously lead to light leakage in that space.